1. Field of Invention
The present invention relates to a material for contact lenses. More particularly, the present invention relates to a silicone hydrogel composition for contact lenses.
2. Description of Related Art
Since contact lenses made from silicone hydrogel have high oxygen permeability, and allows sufficient oxygen directly through the lenses to the cornea, thereby providing sufficient oxygen to the cornea. As such, the silicone hydrogel contact lenses may less likely result in corneal hypoxia from lack of oxygen even after a prolonged wearing of contact lenses. In this regard, silicone hydrogel has become one of the preferable components for making contact lenses.
Silicone hydrogel lenses are typically made from one or two kinds of silicone monomer, macromer or prepolymer, and these silicone components are hydrophobic, so the lens surface is apt to becoming dry due to the lack of water, making eyes feel uncomfortable. There are methods for improving the wettability of a silicone hydrogel lens, such as 1) performing a plasma process on the surface of the silicone-containing hydrophobic lens, which are described in the U.S. Pat. Nos. 6,367,929, 6,822,016, 7,052,131, 7,649,058, 7,666,921, 7,691,916 and 8,168,720. 2) Hydrophilic polymers, such as polyvinylpyrrolidone (PVP), were added to a silicone hydrogel formulation. Further, U.S. publication no. 2006/0063852 disclosed using a silicone-based prepolymer having polyethylene oxide side chains. However, the above methods may make the manufacturing process more difficult and increase the production cost of the silicone hydrogel contact lenses. In addition, silicone hydrogel absorbs lipids easily, so lipids are deposited on the lens surface causing blurred vision.
Therefore, how to polymerize a lens forming composition containing a hydrophilic monomer and a silicone monomer, macromer or prepolymer to obtain a contact lens with high transparency, high oxygen permeability and high moisturizing capability is still an issue to be addressed in the art.